Review of std.signal

[Dicebot]

Time to move forward with some more reviews :)

Our current victim is std.signal by Robert Klotzner which is 
supposed to deprecate and supersede existing (and broken) 
std.signals

--- Input ---

Code: 
https://github.com/phobos-x/phobosx/blob/master/source/phobosx/signal.d
Docs: 
https://vhios.dyndns.org/dlang.org/web/phobos/std_signal.html
Dub package: http://code.dlang.org/packages/phobosx

--- Review format ---

While proposal is expected to be somewhat solid and ready, it is 
a first formal review happening with all previous discussions 
scattered around the various threads (unless I have missed 
something). So intention right now is more to gather some 
destructive input but we may proceed straight to voting if 
reviews will be overwhelmingly positive.

--- Usual information for reviewers ---

Please take this seriously: "If you identify problems along the
way, please note if they are minor, serious, or showstoppers."
(http://wiki.dlang.org/Review/Process). This information later
will be used to determine if library is ready for voting.

If there are any frequent Phobos contributors / core developers
please pay extra attention to submission code style and fitting
into overall Phobos guidelines and structure.